Art of petroleum distillation



Feb. 17, 1925.

T. S. COOKE ART CF PETROLEUM DISTILLA'I'ION Filed Feb. 23, 1918 3 Sheets-Sheet 2 I 17%?6725077' 17%0 03- 61%, dfl' Feb. 17,, 1925.

T. S. COOKE ART OF PETROLEUM DISTILLATION Filed Feb. 23, 1915 Patented Feb. 17,1925.

UNITED STATES PATENT OFFICE.

THOMAS S. COOKE, OF WHITTNG, INDIANA, ASSIGNOR. TO STANDARD OIL COMPANY,

OF CHICAGO, ILLINOIS, A CORPORATION OF INDIANA, 7

ART or PETRoLEUg; DISTILLATION.

Application filed February-23, 1918. 7 Serial No. 218,716.

To all 10h m it may concern.

Be it known that I, THOMAS S; Coons, a citizen of the United States, residing at Whiting, inthe county of Lake and State of Indiana, haveinvented a new and useful Improvement in the Art of Petroleum Distillation, of which the following is a specification.

My invention relates to the art of petroleum distillation and will be full understood from the followingspecification.

In the fractional distillation of crude petroleum as ordinarily practised at the present time there is produced a cut on fraction intermediate gasoline and kerosene,

or between naphtha and refined oil, following the more common usage of the art.

This intermediate out has little or no recognized place in the petroleum products market, being produced-not by design or intermediate fraction was refractionated more or less perfectly by thedirect vaporizing action of steam in stills specially constructed for that purpose and commonly known as steam stills, by reason of which 5 treatment the stock or cut in question received in many refineries the name steam still stock. Probably because of the waste of heat by this method. steam distillation of the cut or stock referred to has now 1 been largely replaced by continuous disa tillation in fire stills.

My invention particularly relates to improvements in such continuous distillation of the stock or cut referred to, the character and origin of which will. it is believed, be'clear to those skilled in the art from the foregoing brief description, it being understood that while the terminology employed herein may be susceptible of other interpretations, it is used in the following specification in the sense defined above.

For the'practise of my invention I employ a' continuous distilling apparatus of the character illustrated diagrammatically in the accompanying drawings. In these drawings i Fig. 1 is a front elevation, partly in section, of a battery of stills.

Fig. 2 is a top plan view.

Fig. 3 is aside elevation, and

Fig. 4: is a longitudinal central section through one of the vapor heat exchangers, taken on the line 4 of Fig. 2. Referring more particularly to the drawings, the four stills which make up the battery illustrated are designated 10 to 13, each still being mounted upon its own setting (the settings shown being for stokerfired furnaces). By the stepped arrangement of the settings the stills are carried at progressively lower levels from'left to right of the series, which. in combination with the constantdevel overflow connections 14 which join each higher still with the next lower still, makes it possible to feed the stock under treatment into the highest still only and permit it to flow continuously through the series to the lowest still undergoing distillation in each of the four stills for an approximately equal period of time. This arrangementand manner of operating the stills themselves is so. well understood in the art as to require no further description. I

The first two stills of the series, i. e., stills 10 and 11 are each provided with a fractionating column of the bubbling-pan type designated 15. As shown in the sectional view (Fig. 1) the column consists of a cylindrical casing. which will preferably be lagged, within which is mounted a, se-

ries of horizontal partitions in theform of pans 1-6. Each an has communication with-the vapor space above the next lower pan through a plurality; of capped nipples, the caps 17 of which extend below the normal liquid level in the an, to form a liquid seal through which t e outgoing vapors must bubble. A constant level is maintained in' each pan through an overflow pipe 18 which extends well below the normal liquid level in the next lower pan.

From the top of each column two vapor lines 19 lead to the inlet chamber 20 of a cylinder. chambers there is led a valved drip conhorizontal tubular. vapor heat exchanger 21, the construction of which is shown in Fig. 4. As isthere illustrated, the vapor tubes are arranged in two sets, a forward set 22 and a rear set 23,'separated by a vaporchamber 24, a third vapor chamber 25 being provided in the rearward end of the From each of the three vapor motion 26, the three connections joining a common drain line 27 which connects at its forward and rearward ends respectively with the column 15eand the final condenser 26 (Fig. 3). Four block valves 27 in the drain line make it possible to direct the condensate from the three vapor chambers back to the column 15 or to the final condenser 26", or; partlyv to one and partly to the other, as desired.

From the last vapor chamber 25 ofthe 7 heat exchanger a vapor line 28 leads to the the omission of the columns thev vapor heat exchangers of these stills may be mounted lower, as shown in Fig. l.

g It is the purpose of the vaporv heat exchangers to transfer the heat of the outgoing vapors to the incoming feed stock. This result is effected by passing this stock through the spaces surrounding the vapor tubes. The incoming stock enters the rear of the exchanger of the first still 10 by a pipe 32, passes over the rear bank oftubes, is transferred around the middle chamber 24 by a bypass-33, and after passing over the front tube-bank is carried by a crossconnection 34 to the next exchanger, through which it follows the same course and thus progressively through the battery. From the last exchanger the heated feed stock is led through a line to the still 10. The cours of the oil through the stills has been heretofore described, From the last still the residue or tar is withdrawn by an overflow connection similar to the connection between the stills The process of distillation as carried out in the above described apparatus in accordance with my invention is as follows: A typical steam still stock is introduced through the feed line 32,. traverses the heat exchangers as described, enters the still 10 in a heated condition and passes through the series of stills. undergoing distillation in Byway of example, a stock of this character may be said to have an initial boiling point of approximately 290 'F. and a maximum boiling point (98% off) of 570 F.- In the operation of the apparatus described, this stock will produce two distillates, a naphtha distillate and a refined oil distillate,

the first of which will be'obtained by mixing the condensate from the stills 10 and 11, and the second from the stills 12 and 13. The naphtha distillate may, with careful. operation, show an initial boiling point of 260 F. and a maximum boiling point of 430 F., while the refined oil distillate will have an initial boiling point of 440 F. and 4 a maximum boiling point of 550 F., the two fractions, refined oil and naphtha, being obtained in approximately equal proportions.

It will be observed from the foregoing example of operation that it is possible by the practice of my invention to actually produce a distinct gap between the maximum boiling point of the naphtha cutand' the initial boiling point ofthe refined oil out, indicating a ver perfect separation and the production 0 a maximum yield of the relatively valuable naphtha.

In contra-distinction to the relatively perfeet separation exemplified by the foregoing, is the ordinary imperfect separation com monly effected by continuous distillation, even where the number of stills in the battery is very great. For example, in a battery of seven stills of the same general type as thestills 12 and 13, illustrated in the drawing, a stock of the characteristics described produces a naphtha cut from the first three stills having an initial boiling point of 265 and a final boiling point of 420; and a refined oil out from the last three stills having an initial 'boiling point of 355 and a final boiling point of 570, with 35% boiling below 420 F. In place of the 10 gap in boiling points attainable by the practice of my invention, it therefore appears that with regard to the first and last three stills alone, and excluding the center still. it is impossible to produce a separation at all comparable with that obtainable by my invention. The distillate from the fourth or middle still of the series of seven referred to showed an initial boiling point of 320 and a maximum boiling point of 500, consisting of approximately 65% naphtha and 35%, refined oil. This distillate from the fourth still, therefore, was very little different from the charging stock itself, and

since it was available neither fornaphtha or refined oil, it was necessarily returned for re-distillation.

' I attribute the sucress of my improved method of distillation to the action of the bubbling-pan fractionating columns 15, which act to accurately separate from the mixed vapors passin from the stills 10 and 11 those fractions tliereof which properly belong in the naphtha cut, returning to the stills the fractions which belong to the re fined oil cut.

Although'it has heretofore been proposed to employ frattionating columns in connection with the distillation of petroleum oils,

I am not aware that any method has heretofore. been devised for taking advantage of the possibilities of the fractionating columns in a commercially feasible manner as is herein suggested, i. e., by providing a series of stills equipped with such columns through which series the oil under treatment is continuously passed. operation'the inherent difficulties with and objections to the use of fractionating'columns for producing the, common commercial petroleum products is overcome.

For simplicity of illustration I have shown a battery comprising only four stills. I prefer, however, to use a much larger number ofstills, forexample, six to ten stills in each battery, and where the charging stock or mixture to be fractionated com prises approximately equal vproportions of the two commercial cuts, as in the steam still stock taken by way of example herein, the proportion between the number of stills equipped with fractionating columns and the number of simple stills should remain approximately as given, i. e., equal numbers of the two varieties of stills. If, on the other hand, the proportion of lighter constituents which it was desired to fractionate from the charging stock were smaller, then the number of the stills in the battery which 'were required to be equipped with the fracout therein with a particular charging stock,

it is to be understood that this is illustra-,

tive only, and for the purpose of making the invention more clear, and that the invention is not limited to these details nor to any of them, except in so far as they are set forth in the following claims, in which it is my in- By this method of oil, comprising a mixture of fractions having a relatively wide range of boiling points, which consists in passing such oil in a con tinuous stream through a series of stills maintained at increasing temperatures in the direction of flow of the oil, subjecting all of the vapors passing from each still to the action of a fItLCtlOIlfltll'lg column, whereby all vapors condensing below a predetermined temperature are condensed in said columns, refluxing to the-stills the vapors condensing in their respective columns in counter-current to the vapors issuing from said stills, and separately condensing and collecting the vapors which escape condensation in the columns, whereby there is obtained from the oil in a single distillation cut having a maximum boiling point not substantially overlapping the initial boiling point of the residue of the oil under treatment.

3. The method of distilling petroleum oils, comprising fractions having a relatively wide range of boiling points, which consists in passing said oil through a series of continuous stills, the stills at theincoming end of the said series being equipped with fractionating columns, while the stllls at the outgoing end are not so equipped, blending the distillates from such firstnamed stills to produce a. cut lighter than the oil under treatment and, having a narrower range of boiling points, and blend ing the distillates from the other stills of the battery to produce a cut heavier than the oil under treatment and havin a narrower range of boiling points, where y the maximum boiling point of the lighter cut may be maintained substantially at or below the ing the distillates from the fractionating column stills to produce a naphtha cut, and blending the distillates from the other stills to produce a refined oil out, the'operation end of the f being conducted so as to avoid substantial lap in boiling points of the cuts. 7

5. The improvement in the art of fractionating petroleum oil products having a continuous ran e of boiling points, which consists in distllling 01? a part of said oil, at least, through a reflux fractionating column, returning to the distilling body of oil only condensate formed in said column in counter-current to the vapors issuing from the still and continuing such distillation until the condensate from the vapors issuing from said column has a desired end boiling point whereby a residue is formed in said still having an initial boilin point substantially higher than the end boiling 'point of said condensate.

6. The improvement in the method of fractionating a petroleum oil of the gasoline-kerosene range of boiling points, which consists in distilling off the gasoline fractions of such oil through'a reflux fractionating column, returning to the distilling'body of oil only condensates formed in said column in counter-curren'txto the vapors issuing from-the still, andcontrolling the distillation to produce a" liquid distillate passing the column and having a desired end boiling point, thereby producing a kerosene residue having an initial boiling point substantiallyv above the end boiling point of said distillate.

7. The improvement in the method of fractionating a petroleum oil of, the gasoline-kerosene range of boiling points, which consists in distilling off the gasoline fractions of such oil through a fractionating column, the condensing zones of which are maintained at such temperatures as to produce a gasoline distillate having an end boiling point substantially lower than the initial boiling point of the undistilled kerosene residue.

7 THOMAS S. COOKE. 

